Use of pyrethroids by California farmers and exterminators has nearly tripled, growing from about 420,000 pounds in 1999 to 1.1 million pounds in 2004. Consumers' retail sales are not included in those numbers but state officials say their usage probably doubles that volume.
Donald Weston, an adjunct professor of integrative biology at UC Berkeley, said his studies have shown that pyrethroids are flowing into storm drains and building up to toxic levels in stream sediment.
Creeks in the Sacramento suburb of Roseville that contain high pyrethroid levels are devoid of tiny crustaceans called \o7hyalella\f7, while nearby streams with low levels are inhabited by them, according to Weston's study, published in October. In lab tests, nearly all samples of the pesticide-tainted sediments from the creeks killed the creatures.
The creatures -- shrimp-like amphipods that live in bottom sediment -- are important prey for small fish, frogs, salamanders and aquatic insects. Their presence is often considered a sign of a healthy waterway.
Weston said that the most toxic compound in the creeks is bifenthrin, which is sprayed around houses by exterminators and is found in some consumer products that are spread on lawns. He did not find pyrethroids from farms or mosquito control in the creeks.
About 20% of the Central Valley's streams contain pyrethroid levels that are toxic to the crustaceans. In addition, they have been detected in creeks in the Monterey area and the Imperial Valley. No tests have been done in the Los Angeles region.
Glenn Brank, a spokesman for the state pesticide department, called the targeting of pyrethroids "definitely the biggest regulatory initiative ever in California involving pesticides and surface waters."
"It will be the kickoff for regulatory oversight for years to come," he said.
In restricting pyrethroids, however, the state agency hopes to keep some as options and ensure that people don't switch to products that wind up being worse.
"We want to do our best to maintain these materials and their viability. They are relatively safe. They don't pose a human health problem like these other materials do," Warmerdam said.
The EPA is also reviewing pyrethroids for possible national restrictions.
Consumers can identify pyrethroids in products by checking labels for compounds that end in "thrin." They are broad spectrum insecticides effective against a wide variety of flying and crawling insects.
State officials said they will be particularly careful in restricting any pyrethroids sprayed by vector control agencies, since combating the West Nile virus, which is spread by mosquitoes, is important.
When manufacturers receive the state notices next month, they must agree within 60 days to begin gathering information about their products' toxicity and buildup in waterways. If they refuse, the agency will immediately cancel their products and they cannot be sold in California.
Labels required by the EPA define how much should be used and prohibit application within 100 feet of waterways. But Warmerdam said the current warnings may be insufficient because consumers now use large volumes.
"The problem is not the material itself. The real challenge is trying to address what appears to be misuse and misapplication ... We may have to eliminate products altogether" or require them in different forms less prone to runoff, she said.
